Display device

ABSTRACT

A display device including a first substrate including a plurality of reflection electrodes on a front side of the first substrate, the plurality of reflection electrodes including a first reflection electrode and a second reflection electrode which is farther away from a light source than the first reflection electrode; a second substrate including a transparent electrode on a back side of the second substrate; a light modulation layer which includes a polymer dispersed liquid crystal layer containing a liquid crystalline monomer and liquid crystal molecules dispersed in the liquid crystalline monomer, the light modulation layer being disposed between the plurality of reflection electrodes and the transparent electrode; a drive section driving the plurality of reflection electrodes and the transparent electrode, wherein an application time of a first drive voltage applied between the transparent electrode and the first reflection electrode is shorter than an application time of a second drive voltage applied between the transparent electrode and the second reflection electrode.

CROSS REFERENCES TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 14/921,060 filed on Oct. 23, 2015, which application claimspriority to Japanese Priority Patent Application JP 2014-245469 filed inthe Japan Patent Office on Dec. 4, 2014, the entire content of which ishereby incorporated by reference.

BACKGROUND

The embodiments discussed herein are related to a display device.

Reflective display devices which perform display by the use of externallight, such as the sunlight, have traditionally been known. Suchreflective display devices perform display by reflecting incident lightfrom the outside by the use of reflection plates. Accordingly, it is noteasy to enhance contrast or improve visibility in a dark place, comparedwith transmissive display devices.

For example, front light type display devices in which a light source isdisposed on this side of a display surface and in which light entersfrom the front are known. Furthermore, semi-transmissive display deviceswhich are fabricated by placing transmission windows in reflectivedisplay devices and in which a backlight disposed on the back side isused are known. In addition, some reflective display devices use displaypanels in which polymer dispersed liquid crystal (PDLC) is used.

See, for example, Japanese Laid-open Patent Publication No. 2012-88486.

SUMMARY

There is provided a display device whose visibility is improved.

According to an aspect, there is provided a display device including alight modulation layer having predetermined refractive index anisotropyand including plural light modulation areas which differ inresponsiveness to an electric field generated by electrodes, apolarization layer which is disposed on a front side of the lightmodulation layer, on which side external light enters, and which shutsout light other than light whose polarization direction is apredetermined polarization direction, a reflection layer disposed on aback side of the light modulation layer, and a phase retardation layerwhich is disposed between the polarization layer and the lightmodulation layer, which creates a predetermined phase difference betweenincident light and reflected light, and which polarizes the reflectedlight in a direction different from the predetermined polarizationdirection, the external light passing through the polarization layer andbecoming the incident light, the incident light being reflected from thereflection layer and becoming the reflected light, the light modulationlayer transmitting the reflected light at the time of the electric fieldnot being generated, the light modulation layer scattering the reflectedlight at the time of the electric field being generated.

The object and advantages of the invention will be realized and attainedby means of the elements and combinations particularly pointed out inthe claims.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and arenot restrictive of the invention.

Additional features and advantages are described herein, and will beapparent from the following Detailed Description and the figures.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a sectional view of an example of the structure of a displaydevice according to a first embodiment;

FIG. 2 illustrates an example of the structure of a display deviceaccording to a second embodiment;

FIG. 3 is a sectional view of an example of the structure of a displaypanel in the second embodiment;

FIGS. 4A and 4B are views for describing a light modulation layer in thesecond embodiment;

FIGS. 5A and 5B are schematic views for describing the function of thelight modulation layer in the second embodiment;

FIG. 6 illustrates the hardware configuration of the display deviceaccording to the second embodiment;

FIG. 7 is a schematic view of reflection display by the display deviceaccording to the second embodiment;

FIG. 8 is a schematic view of light emission display by the displaydevice according to the second embodiment;

FIG. 9 illustrates the structure of a display panel drive section in thesecond embodiment;

FIG. 10 is a sectional view of an example of the structure of a displaypanel included in a display device according to a third embodiment; and

FIG. 11 is a schematic view of light emission display by the displaydevice according to the third embodiment.

DETAILED DESCRIPTION

Embodiments will now be described with reference to the accompanyingdrawings, wherein like reference numerals refer to like elementsthroughout.

Disclosed embodiments are simple examples. It is a matter of course thata proper change which suits the spirit of the invention and which willreadily occur to those skilled in the art falls within the scope of thepresent invention. Furthermore, in order to make description clearer,the width, thickness, shape, or the like of each component mayschematically be illustrated in the drawings compared with the realstate. However, it is a simple example and the interpretation of thepresent invention is not restricted.

In addition, in the present invention and the drawings the samecomponents that have already been described in previous drawings aremarked with the same numerals and detailed descriptions of them may beomitted according to circumstances.

First Embodiment

A display device according to a first embodiment will be described bythe use of FIG. 1. FIG. 1 is a sectional view of an example of thestructure of a display device according to a first embodiment.

A display device 1 according to a first embodiment is a reflectivedisplay device including a light modulation layer 5 sandwiched betweenand held by an upper substrate 4 a and a lower substrate 4 b, apolarization layer 2 disposed on the front side of the light modulationlayer 5, a reflection layer 6 disposed on the back side of the lightmodulation layer 5, and a phase retardation layer 3 disposed between thepolarization layer 2 and the light modulation layer 5. The displaydevice 1 performs display by reflecting external light 8 which entersthe display device 1 by the reflection layer 6. In the followingdescription it is assumed that a side on which the external light 8enters is a front and that the opposite side is a back. Furthermore, itis assumed that light which enters the display device 1 from thepolarization layer 2 and which travels to the reflection layer 6 isincident light and that light which is reflected from the reflectionlayer 6 and which travels to the polarization layer 2 is reflectedlight.

The polarization layer 2 is disposed on the front side of the lightmodulation layer 5 and shuts out light other than light polarized in apredetermined direction. Components of the external light 8, which isnatural light, are shut out by the polarization layer 2, excluding acomponent polarized in the predetermined direction. The polarizationlayer 2 transmits only the component polarized in the predetermineddirection. Incident light polarized in the predetermined directionenters the phase retardation layer 3 in this way. In addition, reflectedlight emitted from the phase retardation layer 3 enters the polarizationlayer 2.

The phase retardation layer 3 is disposed between the polarization layer2 and the light modulation layer 5. The external light 8 passes throughthe polarization layer 2 and becomes the incident light. The incidentlight is reflected from the reflection layer 6. The phase retardationlayer 3 creates a predetermined phase difference between the incidentlight and the reflected light of the incident light. The incident lightemitted from the polarization layer 2 is polarized in the predetermineddirection. A phase difference is created twice, that is to say, at thetime when the incident light enters the phase retardation layer 3 and atthe time when the incident light returns to the phase retardation layer3 as the reflected light. The phase retardation layer 3 shifts the phasetwice. By doing so, the phase retardation layer 3 creates a phasedifference so that the reflected light emitted to the polarization layer2 will be polarized in a direction different from a polarizationdirection of the polarization layer 2.

The upper substrate 4 a and the lower substrate 4 b hold the lightmodulation layer 5 from both sides.

The light modulation layer 5 includes a first light modulation area 5 aand a second light modulation area 5 b each having predeterminedrefractive index anisotropy. The first light modulation area 5 a and thesecond light modulation area 5 b differ in responsiveness to an electricfield generated by electrodes. For example, the responsiveness of thesecond light modulation area 5 b to an electric field is relatively highcompared with the responsiveness of the first light modulation area 5 ato the electric field.

There is little difference in refractive index between the first lightmodulation area 5 a and the second light modulation area 5 b in alldirections including a front direction and an oblique direction when anelectric field is not generated in the above light modulation layer 5.Accordingly, light passes through the light modulation layer 5.

On the other hand, when an electric field is generated in the lightmodulation layer 5, there is a great difference in refractive indexbetween the first light modulation area 5 a and the second lightmodulation area 5 b in all directions. This difference in refractiveindex corresponds to the difference in responsiveness between them. As aresult, reflected light is scattered in the light modulation layer 5. Ascattering degree depends on the intensity of an electric fieldgenerated by electrodes.

The reflection layer 6 reflects the incident light from the lightmodulation layer 5 and returns it to the light modulation layer 5 asreflected light. The reflection layer 6 may be, for example, anelectrode formed on the lower substrate 4 b.

With the display device 1 having the above structure, electrodes areformed so that they will correspond to areas obtained by dividing adisplay surface, and an electric field is controlled. By doing so, eachpixel performs dark display or bright display with one area as onepixel. The dark display is a state in which reflected light is notemitted from the polarization layer 2, and black display is performed.The bright display is a state in which reflected light is emitted fromthe polarization layer 2, and the color of the reflected light isdisplayed. If the external light 8 which is natural light enters, thenwhite display is performed. Furthermore, if a color filter is formed ona path from the light modulation layer 5 to the polarization layer 2along which reflected light travels, the color of the reflected light isconverted by the color filter and a color after the conversion isdisplayed.

The operation of the display device 1 will be described.

When voltage is not applied to electrodes corresponding to a pixel, anelectric field is not generated in the light modulation layer 5.Accordingly, there is no difference in refractive index between thefirst light modulation area 5 a and the second light modulation area 5b. As a result, incident light passes through the light modulation layer5 and enters the phase retardation layer 3 as reflected light. The phaseretardation layer 3 polarizes the reflected light to be emitted to thepolarization layer 2 in a direction different from a polarizationdirection of the polarization layer 2, so the polarization layer 2 doesnot transmit the reflected light. Accordingly, the pixel performs darkdisplay. For example, a λ/4 phase retardation plate may be used as thephase retardation layer 3 which creates a phase difference in the aboveway.

On the other hand, when voltage is applied to the electrodescorresponding to the pixel, an electric field is generated in the lightmodulation layer 5. Accordingly, there is a great difference inrefractive index between the first light modulation area 5 a and thesecond light modulation area 5 b. As a result, incident light andreflected light are scattered in the light modulation layer 5. Part ofscattered light passes through the polarization layer 2 and is emittedto the outside. Accordingly, the pixel performs bright display.

As has been described, the display device 1 is a normally-black modereflective display device. That is to say, when voltage is not appliedto electrodes corresponding to a pixel, the display device 1 performsdark display (black display).

With the display device 1 a pixel performs bright display becausereflected light is scattered in the light modulation layer 5.Furthermore, there is a polarized light component which is notscattered. However, when voltage is applied to electrodes correspondingto a pixel, incident light is converted to linearly polarized light bythe polarization layer 2 and is converted to circularly polarized lightby the phase retardation layer 3. Reflected light of the circularlypolarized light is converted by the phase retardation layer 3 tolinearly polarized light whose polarization direction is the same asthat of the original linearly polarized light, is transmitted by thepolarization layer 2, and is emitted from the polarization layer 2. Thisis the same with ordinary electrically controlled birefringence (ECB)mode. This light emitted from the polarization layer 2 is added to thebright display based on scattered light. As a result, the luminance of apixel is high in the case of bright display, compared with a displaydevice which merely controls the polarization direction of reflectedlight. This improves visibility. In addition, scattering layers havetraditionally been used for increasing luminance. However, there is noneed to form a scattering layer. As a result, a display device becomesthinner.

Second Embodiment

A display device according to a second embodiment will now be described.A display device according to a second embodiment is obtained by addingto the display device 1 according to the first embodiment a light sourcewhich operates in a dark place. The details will now be described.

FIG. 2 illustrates an example of the structure of a display deviceaccording to a second embodiment.

A display device 10 illustrated in FIG. 2 includes an image signaloutput section 11, a signal processing section 12, a display panel 30, adisplay panel drive section 50, a side light source 60, a light sourcedrive section 70, and an optical sensor 80.

The image signal output section 11 outputs an image signal 21 to thesignal processing section 12. Color information corresponding to adisplay block of the display panel 30 is set in the image signal 21.

The signal processing section 12 generates a display signal 22 to bedisplayed on the display panel 30 on the basis of the image signal 21,and outputs the display signal 22 to the display panel drive section 50.The signal processing section 12 performs a correction process on theimage signal 21.

The display panel 30 performs display with each area obtained bydividing the display surface as a unit for display. It is assumed thatthis unit for display is a pixel 40. Pixels 40 are arranged like amatrix to form the display surface.

On the basis of the display signal 22, the display panel drive section50 applies voltage in order to electrodes corresponding to the pixels 40arranged like a matrix. The display panel drive section 50 then controlsthe luminance of the pixels 40 according to the intensity of electricfields generated by applying voltage to the electrodes. The displaypanel drive section 50 is an example of an electrode drive section whichdrives the electrodes corresponding to the pixels 40.

The side light source 60 is disposed along a side of the plane of thedisplay panel 30. When the side light source 60 is driven, the sidelight source 60 makes light enter a light modulation layer from theside.

The light source drive section 70 drives the side light source 60according to ambient illumination detected by the optical sensor 80. Theoptical sensor 80 is an example of an illumination detection sectionwhich detects ambient illumination, and outputs measured ambientillumination to the light source drive section 70. For example, when theoptical sensor 80 detects that the surroundings are bright, the lightsource drive section 70 turns off the side light source 60. As a result,the display device 10 performs reflection display by the use of externallight which enters the display device 10 from the outside. Furthermore,when the optical sensor 80 detects that the surroundings are dark, thelight source drive section 70 drives the side light source 60 to makelight enter the light modulation layer. As a result, the display device10 performs light emission display by the use of light emitted from theside light source 60. Instead of simply turning on or off the side lightsource 60, the light source drive section 70 may change the intensity oflight emitted from the side light source 60 by stages according todetected illumination. Furthermore, one of the following methods may beused. That is to say, the side light source 60 may be turned on or offby the use of an external switch in place of the optical sensor 80.Alternatively, by monitoring power consumption or the status of use, thelight emission intensity of the side light source 60 may properly becontrolled to realize an optimum amount of light.

The structure of the display panel 30 will now be described by the useof FIG. 3. FIG. 3 is a sectional view of an example of the structure ofthe display panel in the second embodiment. In FIG. 3, there is a spacebetween components for the sake of intelligibility. In reality, however,there may be no space between components.

The display panel 30 includes a polarization plate 31, a λ/4 phaseretardation plate 32, an upper substrate 33, a color filter 34, an upperelectrode 35, a light modulation layer 36, a lower electrode 37, and alower substrate 38 laminated in that order from the front side fromwhich external light enters the display panel 30.

The polarization plate 31 transmits a component of incident lightpolarized in a predetermined direction and shuts out the othercomponents of the incident light.

The λ/4 phase retardation plate 32 is an example of the phaseretardation layer 3 in the first embodiment and has the function ofshifting the phase of incident light by a ¼ wavelength. When voltage isnot applied to electrodes corresponding to a pixel 40, the phase ofexternal light shifts by a ¼ wavelength before it enters the displaypanel 30 and after it is reflected. That is to say, the phase ofreflected light which has passed through the λ/4 phase retardation plate32 shifts from the phase of light which has passed through thepolarization plate 31 and which enters the λ/4 phase retardation plate32 by λ/4+λ/4=λ/2. In other words, light polarized in a predetermineddirection as incident light by the polarization plate 31 passes throughthe λ4 phase retardation plate 32 twice, that is to say, when it entersthe display panel 30 and when it is reflected. As a result, the light isconverted to polarized light polarized in a direction different from thepredetermined direction. Accordingly, at this time black display isperformed.

The upper substrate 33 and the lower substrate 38 hold the lightmodulation layer 36 from both sides. At least the upper substrate 33 istransparent to visible light. A material for the upper substrate 33 is aglass plate, a resin substrate, or the like. A reflection layer isformed on the light modulation layer 36 side of the lower substrate 38.Accordingly, the lower substrate 38 may be a transparent substrate ormay not be a transparent substrate. The color filter 34 and the upperelectrode 35 are formed over the upper substrate 33. On the other hand,the lower electrode 37 is formed over the lower substrate 38.

The color filter 34 separates reflected light emitted from the lightmodulation layer 36 into lights of predetermined colors and emits themto the upper substrate 33. In the example of FIG. 3, the pixel 40, whichis a unit for display, is made up of red (R), green (G), and blue (B)color filters included in the color filter 34. An area corresponding toeach color is a subpixel 42. This structure is an example. For example,a pixel may be made up of R, G, B, and white color filters. Furthermore,a pixel may be made up of other color filters, such as a cyan colorfilter, a magenta color filter, and a yellow color filter.

When voltage is applied between the upper electrode 35 and the lowerelectrode 37, an electric field is generated in the light modulationlayer 36 between the upper electrode 35 and the lower electrode 37. Theupper electrode 35 is formed by the use of a transparent material suchas indium tin oxide (ITO). The lower electrode 37 is formed by the useof a metal material or the like and also functions as a reflection platewhich reflects incident light that has passed through the lightmodulation layer 36. The shape of the upper electrode 35 and the lowerelectrode 37 depends on a drive method. Regardless of which drive methodis adopted, however, an electric field can be generated independently inthe light modulation layer 36 with the subpixel 42 as a drive unit. Inthe second embodiment it is assumed that the upper electrode 35 isformed by forming a film on the whole surface (that is to say, shapingis not performed after the formation of a film), that the lowerelectrode 37 corresponds to the subpixel 42, is minute, and has a squareshape, and that each lower electrode 37 is controlled by active matrixdrive. Another drive method, such as simple matrix drive, may beadopted, of course.

The light modulation layer 36 includes light modulation areas of twotypes. The light modulation areas of two types are equal in refractiveindex anisotropy and are different in responsiveness to an electricfield. With the display panel 30 illustrated in FIG. 3, the lightmodulation layer 36 is a composite layer containing a liquid crystallinemonomer 36 a and liquid crystal molecules 36 b dispersed in the liquidcrystalline monomer 36 a. The liquid crystalline monomer 36 a and theliquid crystal molecules 36 b are equal in ordinary refractive index andextraordinary refractive index. For example, refractive index deviationcaused by manufacturing errors or the like is allowable. On the otherhand, the responsiveness of the liquid crystal molecules 36 b to anelectric field is higher than the responsiveness of the liquidcrystalline monomer 36 a to the electric field. For example, the liquidcrystalline monomer 36 a has a striped structure or a porous structurewhich does not respond to an electric field or has a rod-like structurewhose speed of a response to an electric field is slower than the speedof a response of the liquid crystal molecules 36 b to the electricfield. The liquid crystalline monomer 36 a is an example of the firstlight modulation area 5 a and the liquid crystal molecule 36 b is anexample of the second light modulation area 5 b.

The light modulation layer 36 will now be described by the use of FIGS.4A and 4B. FIGS. 4A and 4B are views for describing the light modulationlayer in the second embodiment. FIG. 4A illustrates an example of thestate of the light modulation layer at the time of voltage not beingapplied. FIG. 4B illustrates an example of the state of the lightmodulation layer at the time of voltage being applied. In FIGS. 4A and4B, the refractive index anisotropy of each light modulation areacontained in the light modulation layer 36 is represented by the use ofa refractive index ellipsoid. This refractive index ellipsoid representsthe refractive indices of linearly polarized light which enters fromvarious directions as a tensor ellipsoid. By viewing a section of therefractive index ellipsoid from a direction in which light enters, arefractive index is geometrically known.

As illustrated in FIG. 4A, for example, the direction of an optical axisAX1 of a liquid crystalline monomer 36 a and the direction of an opticalaxis AX2 of a liquid crystal molecule 36 b match (optical axis AX1 ofthe liquid crystalline monomer 36 a and the optical axis AX2 of theliquid crystal molecule 36 b are parallel to each other) in a state inwhich voltage is not applied between a lower electrode 37 and the upperelectrode 35 corresponding to a subpixel 42 and in which an electricfield is not generated in the light modulation layer 36. Each of theoptical axes AX1 and AX2 is parallel to a light traveling directionwhich makes a refractive index constant regardless of a polarizationdirection. There may be a slight deviation between the direction of theoptical axis AX1 and the direction of the optical axis AX2 due tomanufacturing errors or the like.

As illustrated in FIG. 4B, on the other hand, the direction of anoptical axis AX1 of the liquid crystalline monomer 36 a and thedirection of an optical axis AX2 of the liquid crystal molecule 36 bintersect in a state in which voltage is applied between the lowerelectrode 37 and the upper electrode 35 and in which an electric fieldis generated in the light modulation layer 36.

The function of the light modulation layer 36 will be described by theuse of FIGS. 5A and 5B. FIGS. 5A and 5B are schematic views fordescribing the function of the light modulation layer in the secondembodiment. FIG. 5A is a schematic view for describing the function ofthe light modulation layer in a state in which voltage is not applied.FIG. 5B is a schematic view for describing the function of the lightmodulation layer in a state in which voltage is applied. In FIGS. 5A and5B, the upper electrode 35, the lower electrode 37, and the color filter34 are not illustrated. Furthermore, in order to control an electricfield in the light modulation layer 36, the upper electrode 35 and thelower electrode 37 are synchronized and driven by applying voltage. Inthe following description, however, for the sake of simplicity theoperation of generating an electric field may be indicated by theapplication of voltage to electrodes.

In the state of FIG. 5A in which voltage is not applied, voltage is notapplied between the upper electrode 35 and the lower electrode 37 and anelectric field is not generated in the light modulation layer 36. Inthis state, as illustrated in FIG. 4A, the direction of the optical axisAX1 of the liquid crystalline monomer 36 a and the direction of theoptical axis AX2 of the liquid crystal molecule 36 b match and there islittle difference in refractive index in all directions including afront direction and an oblique direction. Accordingly, for example,incident lights L11 a, L11 b, and L11 c which are indicated by chainlines, which are emitted from the side light source 60, and which enterthe light modulation layer 36 from the side pass through the lightmodulation layer 36 without being scattered in the light modulationlayer 36. Light which is emitted from the side light source 60 and whichtravels to the lower substrate 38 or the upper substrate 33 is totallyreflected and is not emitted to the outside. As has been described, whenvoltage is not applied between the upper electrode 35 and the lowerelectrode 37, the light modulation layer 36 does not emit light emittedfrom the side light source 60 to the upper substrate 33 side. As aresult, dark display is performed on the display surface.

In the state of FIG. 5B in which voltage is applied, on the other hand,voltage is applied between the upper electrode 35 and the lowerelectrode 37 and an electric field is generated in the light modulationlayer 36. In this state, as illustrated in FIG. 4B, the direction of theoptical axis AX1 of the liquid crystalline monomer 36 a and thedirection of the optical axis AX2 of the liquid crystal molecule 36 bintersect and there is a great difference in refractive index in alldirections including a front direction and an oblique direction. As aresult, a powerful scattering property is obtained. For example,incident lights L12 a, L12 b, and L12 c which are emitted from the sidelight source 60 and which enter the light modulation layer 36 from theside are scattered in the light modulation layer 36 and scattered lightsL31 and L32 are emitted from the upper substrate 33. As a result,scattered light which has passed through the upper substrate 33 ispolarized in all directions. Part of the scattered light passes throughthe polarization plate 31 and is emitted to the outside.

It is assumed that the side light source 60 included in the displaydevice 10 having the above structure is driven in a dark place. In astate in which voltage is not applied to electrodes corresponding to asubpixel 42, as illustrated in FIG. 5A, light emitted from the sidelight source 60 passes through the light modulation layer 36 in adirection parallel to the display surface and is not emitted from theupper substrate 33. On the other hand, in a state in which voltage isapplied to the electrodes corresponding to the subpixel 42, asillustrated in FIG. 5B, light emitted from the side light source 60 isscattered in the light modulation layer 36 and part of scattered lightis emitted from the upper substrate 33.

In FIGS. 5A and 5B, a case where light emitted from the side lightsource 60 enters the light modulation layer 36 from the side isdescribed. However, the same applies to external light which enters thelight modulation layer 36 from the front side. That is to say, in astate in which voltage is not applied to corresponding electrodes and anelectric field is not generated in the light modulation layer 36, blackdisplay is performed. In a state in which voltage is applied tocorresponding electrodes and an electric field is generated in the lightmodulation layer 36, bright display is performed.

The display device 10 operates in this way in normally black mode.

The hardware configuration will now be described by the use of FIG. 6.FIG. 6 illustrates the hardware configuration of the display deviceaccording to the second embodiment.

The whole of the display device 10 is controlled by a control section90. The control section 90 includes a central processing unit (CPU) 91.A random access memory (RAM) 92, a read only memory (ROM) 93, and aplurality of peripheral units are coupled to the CPU 91 via a bus 96.

The CPU 91 is a processor which realizes the processing functions of thecontrol section 90.

The RAM 92 is used as main storage of the control section 90. The RAM 92temporarily stores at least part of an operating system (OS) program oran application program executed by the CPU 91. In addition, the RAM 92stores various pieces of data which the CPU 91 needs to perform aprocess.

The ROM 93 is a read only semiconductor memory and stores the OSprogram, application programs, and fixed data which is not rewritten.Furthermore, a semiconductor memory, such as a flash memory, may be usedas auxiliary storage in place of or in addition to the ROM 93.

The plurality of peripheral units coupled to the bus 96 are the displaypanel drive section 50, the light source drive section 70, the opticalsensor 80, an input interface 94, and a communication interface 95.

The display panel 30 is coupled to the display panel drive section 50.

The side light source 60 is coupled to the light source drive section70.

The optical sensor 80 informs the CPU 101 or the light source drivesection 70 via the bus 96 of measured illumination.

An input device used for inputting a user's instructions and aninterface used for acquiring an image signal from another apparatus arecoupled to the input interface 94. The input interface 94 transmits tothe CPU 91 a signal transmitted from the input device or anotherapparatus.

The communication interface 95 is coupled to a network 98. Thecommunication interface 95 transmits data to or receives data fromanother computer or a communication apparatus via the network 98.

By adopting the above hardware configuration, the processing functionsin the second embodiment are realized. The above configuration is anexample and is changed properly.

The processing functions of the image signal output section 11 and thesignal processing section 12 illustrated in FIG. 2 are realized by thecontrol section 90.

The operation of the display device 10 having the above structure willbe described.

The display device 10 measures ambient illumination by the opticalsensor 80 and turns on or off the side light source 60 according to theillumination detected by the optical sensor 80. In a bright place thedisplay device 10 turns off the side light source 60 and performsreflection display by the use of external light which enters the displaydevice 10 from the outside. In a dark place the display device 10 turnson the side light source 60 and performs light emission display by theuse of light emitted from the side light source 60. Furthermore, one ofthe following methods may be used. That is to say, the side light source60 may be turned on or off by the use of an external switch in place ofthe optical sensor 80. Alternatively, by monitoring power consumption orthe status of use, the light emission intensity of the side light source60 may properly be controlled to realize an optimum amount of light.

Reflection display and light emission display by the display device 10will now be described by the use of FIGS. 7 and 8. Components in FIGS. 7and 8 which are the same as those illustrated in FIG. 3 are marked withthe same numerals and their descriptions will be omitted.

The reflection display which is performed in a bright place with theside light source 60 turned off will be described first. FIG. 7 is aschematic view of reflection display by the display device according tothe second embodiment. A dashed line in FIG. 7 indicates an area of eachsubpixel.

External lights L21 and L22 which enter the display panel 30 from theoutside are reflected from the lower electrode 37 which also functionsas a reflection plate and reflected lights obtained in this way are usedfor performing the reflection display.

In the example of FIG. 7, a subpixel 43 a is in a state in which voltageis not applied to corresponding electrodes and a subpixel 43 b is in astate in which voltage is applied to corresponding electrodes.

In the light modulation layer 36 corresponding to the subpixel 43 a in astate in which voltage is not applied to the corresponding electrodes,the direction of an optical axis of the liquid crystalline monomer 36 aand the direction of an optical axis of a liquid crystal molecule 36 bmatch and there is little difference in refractive index. Accordingly,the external light L21 which enters an area of the light modulationlayer 36 corresponding to the subpixel 43 a travels to the lowerelectrode 37 without being scattered, and is reflected. Similarly,reflected light of the external light L21 travels to the λ/4 phaseretardation plate 32 without being scattered. The phase is shifted bythe λ/4 phase retardation plate 32 twice, that is to say, when theexternal light L21 enters the display panel 30 and when the externallight L21 is reflected. As a result, the reflected light which haspassed through the λ/4 phase retardation plate 32 is polarized in adirection different from a polarization direction of the polarizationplate 31. Therefore, the reflected light which has passed through theλ/4 phase retardation plate 32 is not emitted from the polarizationplate 31. That is to say, the subpixel 43 a performs black display.

In the light modulation layer 36 corresponding to the subpixel 43 b in astate in which voltage is applied to the corresponding electrodes, thedirection of an optical axis of the liquid crystalline monomer 36 a andthe direction of an optical axis of a liquid crystal molecule 36 bdiffer from each other, so there is a great difference in refractiveindex in all directions. As a result, reflected light is scattered inthe light modulation layer 36. Part of components of scattered light L33which travel to the front side pass through the color filter 34 and areemitted from the polarization plate 31. A blue color filter is disposedin an area of the color filter 34 corresponding to the subpixel 43 b, sothe subpixel 43 b displays blue (B). Furthermore, there is a polarizedlight component which is not scattered. However, when voltage is appliedto electrodes corresponding to a pixel, incident light is converted tolinearly polarized light by the polarization plate 31 and is convertedto circularly polarized light by the λ/4 phase retardation plate 32.Reflected light of the circularly polarized light is converted by theλ/4 phase retardation plate 32 to linearly polarized light whosepolarization direction is the same as that of the original linearlypolarized light, is transmitted by the polarization plate 31, and isemitted from the polarization plate 31. This is the same with theordinary ECB mode. The light emitted from the polarization plate 31 isadded to bright display based on scattered light.

The light emission display which is performed in a dark place with theside light source 60 turned on will be described next. FIG. 8 is aschematic view of light emission display by the display device accordingto the second embodiment. A dashed line in FIG. 8 indicates an area ofeach subpixel.

Light source light L13 emitted from the side light source 60 is used forperforming light emission display.

In the example of FIG. 8, a subpixel 44 a is in a state in which voltageis not applied to corresponding electrodes and a subpixel 44 b is in astate in which voltage is applied to corresponding electrodes. The lightsource light L13 emitted from the side light source 60 is totallyreflected repeatedly from the upper substrate 33 and the lower electrode37 and travels in a horizontal direction in FIG. 8.

In the light modulation layer 36 corresponding to the subpixel 44 a in astate in which voltage is not applied to the corresponding electrodes,the direction of an optical axis of the liquid crystalline monomer 36 aand the direction of an optical axis of a liquid crystal molecule 36 bmatch and there is little difference in refractive index. Accordingly,the light source light L13 passes through an area of the lightmodulation layer 36 corresponding to the subpixel 44 a without beingscattered. As a result, light is not emitted from the subpixel 44 a andthe subpixel 44 a performs black display.

In the light modulation layer 36 corresponding to the subpixel 44 b in astate in which voltage is applied to the corresponding electrodes, thedirection of an optical axis of the liquid crystalline monomer 36 a andthe direction of an optical axis of a liquid crystal molecule 36 bdiffer from each other, so there is a great difference in refractiveindex in all directions. As a result, the light source light L13 whichenters an area of the light modulation layer 36 corresponding to thesubpixel 44 b is scattered. Part of components of scattered light L34which travel to the front side pass through the color filter 34 and areemitted from the polarization plate 31. A green color filter is disposedin an area of the color filter 34 corresponding to the subpixel 44 b, sothe subpixel 44 b displays green (G).

As has been described, the display device 10 includes the lightmodulation layer 36 which transmits incident light at the time ofvoltage not being applied to electrodes and which scatters incidentlight at the time of voltage being applied to electrodes. As a result,the display device 10 performs reflection display and light emissiondisplay in the normally black mode. With bright display in which a colorof the color filter 34 is displayed, light is scattered in the lightmodulation layer 36. Accordingly, the display device 10 can realize highluminance, compared with a display device which performs bright displayonly by manipulating the polarization direction of reflected light.

In the above description the reflection display and the light emissiondisplay are separated. However, the display device 10 can performreflection display and light emission display at the same time. Asillustrated in FIGS. 7 and 8, for example, the subpixels 43 a and 44 ain a state in which voltage is not applied to the correspondingelectrodes transmit the external light L21 and the light source lightL13 and do not emit the external light L21 and the light source lightL13, respectively, to the outside. The subpixels 43 b and 44 b in astate in which voltage is applied to the corresponding electrodesscatter external light L22 and the light source light L13, respectively,and emit lights which pass through the color filter 34.

Therefore, for example, even if the intensity of light emitted from theside light source 60 to the light modulation layer 36 is changed bystages according to ambient illumination obtained from the opticalsensor 80, a high luminance image is obtained in bright display.Furthermore, with the display device 10 it is possible to enhancecontrast by high luminance in bright display. This improves visibility.

By the way, with the display device 10 the side light source 60 isdisposed at an end of the light modulation layer 36. Accordingly, thereis a tendency for the luminance of each pixel 40 obtained from the sidelight source 60 to increase as the distance from the side light source60 decreases and to decrease as the distance from the side light source60 increases.

Therefore, when the display device 10 turns on the side light source 60to perform light emission display, the display device 10 driveselectrodes corresponding to each pixel 40 on the basis of colorinformation for each pixel 40 based on an image signal and the luminanceof each pixel 40 obtained from the side light source 60. For example,when the display device 10 drives electrodes in light emission display,the display device 10 may estimate the amount of a decrease in theluminance of each pixel 40 caused by an increase in the distance fromthe side light source 60 and correct gradation values of the displaysignal 22, drive voltage applied to electrodes, or drive time accordingto the amount of a decrease in the luminance of each pixel 40.Alternatively, the structure of electrodes may be changed according tothe distance from the side light source 60. These techniques will now bedescribed in order.

First the technique of controlling the driving of electrodescorresponding to a pixel 40 according to the distance between the sidelight source 60 and the pixel 40 will be described. Correction made bythe display panel drive section 50 will be described as an example.

FIG. 9 illustrates the structure of the display panel drive section inthe second embodiment. Components in FIG. 9 which are the same as thoseillustrated in FIG. 2 are marked with the same numerals and theirdescriptions will be omitted.

The display panel drive section 50 includes a switching block 51, acorrection block 52, and a drive circuit 53. Furthermore, in the exampleof FIG. 9, a command receiving section 13 which transmits a user'sinstructions to the light source drive section 70 is included.

The switching block 51 switches the operation mode of the display paneldrive section 50 to light emission display or reflection display. Asignal which is indicative of whether the side light source 60 is on oroff is inputted from the light source drive section 70 to the switchingblock 51. The switching block 51 determines on the basis of this signalwhether or not the side light source 60 is on. When the side lightsource 60 is off, the switching block 51 selects reflection display.When the side light source 60 is on, the switching block 51 selectslight emission display.

When the switching block 51 selects reflection display, the displaysignal 22 is transmitted to the drive circuit 53. Furthermore, when theswitching block 51 selects light emission display, the display signal 22is transmitted to the correction block 52 to make correction. In thefollowing description it is assumed that a signal which is outputted tothe drive circuit 53 via the correction block 52 at the time of theswitching block 51 selecting light emission display is a signal forlight emission display and that a signal which is outputted to the drivecircuit 53 at the time of the switching block 51 selecting reflectiondisplay is a signal for reflection display.

When the display signal 22 is inputted to the correction block 52 viathe switching block 51, the correction block 52 corrects the displaysignal 22 according to the luminance of a target pixel 40 obtained fromthe side light source 60, and outputs it to the drive circuit 53 as asignal for light emission display. When the switching block 51 selectsreflection display, the correction block 52 may stop processing.

The signal for light emission display or a signal for reflection displayselected by the switching block 51 is inputted to the drive circuit 53.The drive circuit 53 controls the driving of the display panel 30 on thebasis of the signal for light emission display inputted from thecorrection block 52 or the signal for reflection display.

The command receiving section 13 accepts an operation command regardingdriving the side light source 60, such as turning on or off the sidelight source 60, and informs the light source drive section 70 about thecontents of the operation command.

The correction block 52 will be described. The correction block 52 makesa correction according to the luminance of a target pixel 40 obtainedfrom the side light source 60 on the basis of the display signal 22 forthe target pixel 40 and the distance between the target pixel 40 and theside light source 60.

One method is to divide the display area into several blocks accordingto the distance from the side light source 60 and to control drivevoltage to be applied to electrodes according to blocks. For example,drive voltage for displaying white is determined in advance for eachblock. This drive voltage is determined in advance so as to establishthe relationship

V1<V2<. . . <Vn   (1)

where V1 is white display voltage for a pixel in a block which is theclosest to the side light source 60, V2 is white display voltage for apixel in a block which is the second closest to the side light source60, and Vn is white display voltage for a pixel in an nth (n is anyinteger) block which is the most distant from the side light source 60.

The correction block 52 acquires white display voltage for a block towhich the target pixel 40 belongs, and corrects the display signal 22for the target pixel 40 on the basis of the white display voltage togenerate a signal for light emission display. For example, thecorrection block 52 finds the signal for light emission display byadding a correction amount corresponding to the white display voltage togradation values of the display signal 22.

Alternatively, the signal for light emission display may designate atleast one of drive voltage and drive time at the time of the drivecircuit 53 applying voltage to electrodes corresponding to the targetpixel 40.

With inequality (1) white display voltage is determined in advanceaccording to blocks. However, white display voltage may be determined inadvance according to pixel columns. A pixel column means a column ofpixels arranged in a direction parallel to a side of the display surfacebeside which the side light source 60 is disposed.

Furthermore, a correction may be made by the use of luminanceinformation in which information regarding luminance obtained for eachpixel 40 is associated with the distance between each pixel 40 and theside light source 60 or the position of each pixel 40 and which isstored in advance. Furthermore, for example, information regarding whitedisplay voltage associated with each pixel 40 may be stored in advancein place of the luminance information. In addition, informationregarding an optimum correction amount may be stored in advance. Thesepieces of table information may be stored in advance by associating themwith the blocks or the pixel columns.

With the above method white display voltage is set for each block oreach pixel column. However, luminance distribution may be analyzed andwhite display voltage may be considered as a function of the distancebetween a pixel and the side light source 60. For example, white displayvoltage Vm for any pixel m is defined by

Vm=Vx−LOG(d)   (2)

where Vx is white display voltage for a pixel x which is the mostdistant from the side light source 60, and d is the distance (number ofpixels) between the pixel m and the pixel x.

According to expression (2), the white display voltage Vx for the pixelx which is the most distant from the side light source 60 is the maximumdrive voltage and the white display voltage Vm falls as the distancefrom the side light source 60 decreases.

As has been described, with light emission display using the side lightsource 60, gradation values, drive voltage, or drive time is correctedaccording to the luminance of a target pixel 40 obtained from the sidelight source 60 to compensate for the amount of a decrease in luminance.By doing so, display having high visibility and, for example, littlecolor irregularity is obtained.

With the above technique the display panel drive section 50 correctsdrive voltage or drive time at the time of driving electrodescorresponding to a target pixel 40 or gradation values or the like.

On the other hand, it is possible to compensate for the amount of adecrease in luminance corresponding to the distance from the side lightsource 60 by changing the structure of electrodes. For example,electrode area may be changed according to the distance from the sidelight source 60. That is to say, the area of an electrode which is themost distant from the side light source 60 is maximized and the area ofan electrode which is the closest to the side light source 60 isminimized. An increase in electrode area leads to an increase in area ofthe light modulation layer 36 in which light is scattered. As a result,high luminance is obtained compared with an area where electrode area issmall.

Third Embodiment

A display device according to a third embodiment will now be described.The display device 10 according to the second embodiment includes theside light source 60 as a light source which operates in a dark place.However, a display device according to a third embodiment includes afront light as a light source. A display device according to a thirdembodiment is realized by replacing the display device 10 according tothe second embodiment with a front light type display device, and is thesame as the display device 10 according to the second embodimentillustrated in FIGS. 2 and 3 in the other respects.

As described in the second embodiment, the use of the side light source60 has the effect of reducing the thickness of the display device 10. Onthe other hand, there may be need to reduce not the thickness but thearea of the display device 10. A display device according to a thirdembodiment is suitable for such a case.

The structure of a display device according to a third embodiment willbe described by the use of FIG. 10. FIG. 10 is a sectional view of anexample of the structure of a display panel included in a display deviceaccording to a third embodiment. Components in FIG. 10 which are thesame as those illustrated in FIG. 2 or 3 are marked with the samenumerals and their descriptions will be omitted. FIG. 10 alsoillustrates reflection display performed by a display device accordingto a third embodiment.

A display panel 300 included in a display device according to a thirdembodiment includes a polarization plate 31, a λ/4 phase retardationplate 32, an upper substrate 33, a color filter 34, an upper electrode35, a light modulation layer 36, a lower electrode 37, and a lowersubstrate 38 which are laminated. This is the same with the displaypanel 30 included in the display device 10 according to the secondembodiment. The display panel 300 differs from the display panel 30 inthat a light guide plate 302 is disposed on the front side of thepolarization plate 31 in place of the side light source 60 and in that afront light 301 is disposed as a light source near one end of the lightguide plate 302. Switching between light emission display and reflectiondisplay is determined according to ambient illumination detected by anoptical sensor 80. This is the same with the second embodiment. That isto say, the display device according to the third embodiment performsreflection display in a bright place with the front light 301 turnedoff. On the other hand, the display device according to the thirdembodiment performs light emission display in a dark place with thefront light 301 turned on. The front light 301 may be turned on or offby the use of an external switch in place of the optical sensor 80.Alternatively, by monitoring power consumption or the status of use, thelight emission intensity of the front light 301 may properly becontrolled to realize an optimum amount of light.

Reflection display performed with the front light turned off will bedescribed by the use of FIG. 10. The display device according to thethird embodiment performs reflection display in the same way as with thedisplay device 10 illustrated in FIG. 7, excluding the fact that thelight guide plate 302 is disposed on the front side of the polarizationplate 31. That is to say, in a subpixel 45 a in a state in which voltageis not applied to corresponding electrodes, external light L23 passesthrough the polarization plate 31 and is polarized. The phase of theexternal light L23 is then shifted by a ¼ wavelength by the λ/4 phaseretardation plate 32 and the external light L23 enters the lightmodulation layer 36. In the light modulation layer 36 corresponding tothe subpixel 45 a in which an electric field is not generated, theincident light is reflected. The phase of reflected light is shiftedfurther by a ¼ wavelength by the λ/4 phase retardation plate 32 and thereflected light enters the polarization plate 31. The reflected light isshut out by the polarization plate 31, so the subpixel 45 a performsblack display. In a subpixel 45 b in a state in which voltage is appliedto corresponding electrodes, on the other hand, reflected light isscattered in the light modulation layer 36 and part of scattered lightpasses through the color filter 34, the λ/4 phase retardation plate 32,and the polarization plate 31 and is emitted. As a result, the subpixel45 b displays a color of the color filter 34.

Next, light emission display performed with the front light turned onwill be described. FIG. 11 is a schematic view of light emission displayby the display device according to the third embodiment. A dashed linein FIG. 11 indicates an area of each subpixel.

Light source light L14 emitted from the front light 301 is used forperforming light emission display.

In the example of FIG. 11, a subpixel 46 a is in a state in whichvoltage is not applied to corresponding electrodes and a subpixel 46 bis in a state in which voltage is applied to corresponding electrodes.The light source light L14 emitted from the front light 301 is totallyreflected repeatedly in the light guide plate 302 and travels in ahorizontal direction in FIG. 11.

Part of the light source light L14 then enters the polarization plate 31from the light guide plate 302. As a result, with the display deviceaccording to the third embodiment including the front light 301 and thelight guide plate 302, operation in light emission display is the sameas that in reflection display illustrated in FIG. 10. That is to say,the subpixel 46 a in a state in which voltage is not applied to thecorresponding electrodes performs black display and the subpixel 46 b ina state in which voltage is applied to the corresponding electrodesdisplays a corresponding color of the color filter 34.

As has been described, the side light source 60 may be replaced with thefront light 301 and the light guide plate 302. With the display deviceaccording to the third embodiment light is scattered in the lightmodulation layer 36 in bright display. This is the same with the displaydevice 10 according to the second embodiment. Accordingly, highluminance is obtained and a display device with high visibility isrealized.

The above processing functions can be realized with a computer. In thatcase, a program in which the contents of the functions that the displaydevice has are described is provided. By executing this program on thecomputer, the above processing functions are realized on the computer.This program may be recorded on a computer readable record medium. Acomputer readable record medium may be a magnetic storage device, anoptical disk, a magneto-optical recording medium, a semiconductormemory, or the like. A magnetic storage device may be a hard disk drive(HDD), a flexible disk (FD), a magnetic tape, or the like. An opticaldisk may be a digital versatile disc (DVD), a DVD-RAM, a compactdisc(CD)-ROM, a CD-recordable(R)/rewritable(RW), or the like. Amagneto-optical recording medium may be a magneto-optical disk (MO) orthe like.

To place the program on the market, portable record media, such as DVDsor CD-ROMs, on which it is recorded are sold. Alternatively, the programis stored in advance in a storage unit of a server computer and istransferred from the server computer to another computer via a network.

When a computer executes this program, it will store the program, whichis recorded on a portable record medium or which is transferred from theserver computer, in, for example, its storage unit. Then the computerreads the program from its storage unit and performs processes incompliance with the program. The computer may read the program directlyfrom a portable record medium and perform processes in compliance withthe program. Furthermore, each time the program is transferred from theserver computer connected via a network, the computer may performprocesses in order in compliance with the program it receives.

In addition, at least part of the above processing functions may berealized by an electronic circuit such as a digital signal processor(DSP), an application specific integrated circuit (ASIC), or aprogrammable logic device (PLD).

Various changes and modifications which fall within the scope of theconcept of the present disclosure are conceivable by those skilled inthe art and it is understood that these changes and modifications fallwithin the scope of the present disclosure. For example, those skilledin the art may add components to, delete components from, or makechanges in the design of components in each of the above embodimentsaccording to circumstances, or may add processes to, omit processesfrom, or make changes in conditions in processes in each of the aboveembodiments according to circumstances. These additions, deletions,changes, and omissions fall within the scope of the present disclosureas long as they include the essentials of the present disclosure.

The present disclosure includes the following aspects.

(1) A display device including: a light modulation layer havingpredetermined refractive index anisotropy and including plural lightmodulation areas which differ in responsiveness to an electric fieldgenerated by electrodes; a polarization layer which is disposed on afront side of the light modulation layer, on which side external lightenters, and which shuts out light other than light whose polarizationdirection is a predetermined polarization direction; a reflection layerdisposed on a back side of the light modulation layer; and a phaseretardation layer which is disposed between the polarization layer andthe light modulation layer, which creates a predetermined phasedifference between incident light and reflected light, and whichpolarizes the reflected light in a direction different from thepredetermined polarization direction, the external light passing throughthe polarization layer and the incident light being generated, theincident light being reflected from the reflection layer and thereflected light being generated, wherein: when the electric field is notgenerated, the light modulation layer transmits the reflected light; andwhen the electric field is generated, the light modulation layerscatters the reflected light.

(2) The display device according to (1) further including: a first lightsource which makes light enter the light modulation layer from a side ofthe light modulation layer; and a first light source drive section whichdrives the first light source, wherein: when the first light sourcedrive section turns on the first light source, light emitted from thefirst light source enters the light modulation layer, and the electricfield is not generated, the light modulation layer transmits the lightemitted from the first light source; and when the first light sourcedrive section turns on the first light source, light emitted from thefirst light source enters the light modulation layer, and the electricfield is generated, the light modulation layer scatters the lightemitted from the first light source.

(3) The display device according to (2) further including anillumination detection section which detects ambient illumination,wherein the first light source drive section controls the driving of thefirst light source according to illumination detected by theillumination detection section.

(4) The display device according to (2) or (3) further including anelectrode drive section which acquires an image signal including colorinformation for a pixel, which is a unit for display, and which driveselectrodes corresponding to the pixel on the basis of the image signal,wherein when the first light source is on, the electrode drive sectiondrives the electrodes corresponding to the pixel on the basis ofluminance of the pixel obtained from the first light source and theimage signal for the pixel.

(5) The display device according to (4), wherein the electrode drivesection corrects at least one of drive voltage to be applied to theelectrodes and drive time obtained from the image signal on the basis ofan amount of a decrease in the luminance of the pixel obtained from thefirst light source which is caused by an increase in distance from thefirst light source and drives the electrodes.

(6) The display device according to (4), wherein the electrode drivesection corrects a gradation value included in the image signal on thebasis of an amount of a decrease in the luminance of the pixel obtainedfrom the first light source which is caused by an increase in distancefrom the first light source and drives the electrodes.

(7) The display device according to (4), wherein: the electrodes differin distance from the first light source; and an area of a firstelectrode is larger than an area of a second electrode which is closerto the first light source than the first electrode.

(8) The display device according to any of (4) to (7), wherein theelectrode drive section: stores in advance luminance informationcorresponding to the luminance of the pixel obtained from the firstlight source; and drives the electrodes by the use of the luminanceinformation.

(9) The display device according to (1) further including: a secondlight source which makes light enter the polarization layer from a frontside; a light guide plate which transmits light emitted from the secondlight source to an entire surface of the polarization layer; and asecond light source drive section which drives the second light source.

All examples and conditional language provided herein are intended forthe pedagogical purposes of aiding the reader in understanding theinvention and the concepts contributed by the inventor to further theart, and are not to be construed as limitations to such specificallyrecited examples and conditions, nor does the organization of suchexamples in the specification relate to a showing of the superiority andinferiority of the invention. Although one or more embodiments of thepresent invention have been described in detail, it should be understoodthat various changes, substitutions, and alterations could be madehereto without departing from the spirit and scope of the invention.

It should be understood that various changes and modifications to thepresently preferred embodiments described herein will be apparent tothose skilled in the art. Such changes and modifications can be madewithout departing from the spirit and scope of the present subjectmatter and without diminishing its intended advantages. It is thereforeintended that such changes and modifications be covered by the appendedclaims.

The invention is claimed as follows:
 1. A display device comprising: afirst substrate including a plurality of reflection electrodes on afront side of the first substrate, the plurality of reflectionelectrodes including a first reflection electrode and a secondreflection electrode which is farther away from a light source than thefirst reflection electrode; a second substrate including a transparentelectrode on a back side of the second substrate; a light modulationlayer which includes a polymer dispersed liquid crystal layer containinga liquid crystalline monomer and liquid crystal molecules dispersed inthe liquid crystalline monomer, the light modulation layer beingdisposed between the plurality of reflection electrodes and thetransparent electrode; a drive section driving the plurality ofreflection electrodes and the transparent electrode, wherein anapplication time of a first drive voltage applied between thetransparent electrode and the first reflection electrode is shorter thanan application time of a second drive voltage applied between thetransparent electrode and the second reflection electrode.
 2. Thedisplay device according to claim 1, further comprising a polarizationlayer which is disposed on a front side of the second substrate.
 3. Thedisplay device according to claim 2, further comprising a phaseretardation layer disposed between the polarization layer and the secondsubstrate, which creates a predetermined phase difference betweenincident light and reflected light, and which polarizes the reflectedlight in a direction different from a predetermined polarizationdirection, the external light passing through the polarization layer andbecoming the incident light, the incident light being reflected from theplurality of reflection electrodes and becoming the reflected light. 4.The display device according to claim 2, further comprising anillumination detection section which detects ambient illumination,wherein: when the illumination detected by the illumination detectionsection is more than a predetermined value, a light source drive sectionturns off the light source; and when the illumination detected by theillumination detection section is less than the predetermined value, thelight source drive section turns on the light source.
 5. The displaydevice according to claim 3, further comprising an illuminationdetection section which detects ambient illumination, wherein: when theillumination detected by the illumination detection section is more thana predetermined value, a light source drive section turns off the lightsource; and when the illumination detected by the illumination detectionsection is less than the predetermined value, the light source drivesection turns on the light source.
 6. The display device according toclaim 4, wherein an electrode drive section corrects a gradation valueincluded in an image signal supplied to the electrode drive section onthe basis of an amount of a decrease in the luminance which is caused byan increase in distance from the light source and drives the electrodes.7. The display device according to claim 1, wherein an area of the firstreflection electrode is smaller than an area of the second reflectionelectrode.
 8. The display device according to claim 6, wherein theelectrode drive section: stores in advance luminance informationcorresponding to the luminance; and drives the electrodes by the use ofthe luminance information.